NEW YORK — A brief power outage darkened a large swath of Manhattan and the Bronx Wednesday, knocking out traffic lights, cutting subway service and forcing the evacuation of the Metropolitan Museum of Art on one of the hottest days of the year.

ADAM GOLDMAN

NEW YORK — A brief power outage darkened a large swath of Manhattan and the Bronx Wednesday, knocking out traffic lights, cutting subway service and forcing the evacuation of the Metropolitan Museum of Art on one of the hottest days of the year.

Power was restored within about an hour, but that did not stop the city from experiencing some of the chaos it endured during blackouts last year and in 2003.

The Metropolitan Museum of Art was evacuated, and visitors were forced to sit on the outside steps in the sweltering heat. Traffic lights up and down the east side of Manhattan and the Bronx, including the area around Yankee Stadium, went dark.

The city was in the second day of temperatures well over 90 degrees.

"People came in off the street and we were selling flashlights, bottled water, candles, ice," said Barry Newman, a pharmacist at a Gristede's Pharmacy on the Upper East Side.

Consolidated Edison said the blackout affected 136,700 customers in all, or more than 500,000 people.

The cause was under investigation, but utility spokesman Chris Olert said it was some sort of transmission disturbance. He didn't know whether the heat was a factor. "We won't even speculate on the cause yet," Olert said.

Suspensions and delays were reported along the city's subways because of the power failure. The Metro-North commuter railroad, which serves the northern suburbs, had to reduce the number of trains it was using, resulting in delays and crowded trains as the evening rush-hour approached, said spokeswoman Marjorie Anders.

The power outage was reminiscent of previous summer blackouts that struck New York City.

Last summer, about 174,000 people were affected by a blackout in Queens. Residents sweltered without air conditioners on some of the hottest days of the year, and estimated business losses ran into the tens of millions of dollars as stores were forced to throw out perished goods.

The Public Service Commission issued a blistering report this year, and said the company needed to make "critical and substantial" improvements.

New York was also hard hit by a 2003 blackout that cut power to a large chunk of the Northeast.